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Show STEAM-ENGINE. NoTE XI. yellow and rancid; if it be wa01ed with much cold wa~er a.fter it has imbibed .the fal.t, and jufl: before it is hung up, I am well informed, that 1t will not become rancid, or tn very flight degrees. In the former cafe I imagine the fait on the furf~ce of the bacon attraCl:s water during the cold of the night, which is evaporated du~mg the ~:~y, nnd that in this evaporation a part of the water becomes decompofe.d, as m ~Jeachtng, and its vital air tmiting with greater facility in its unehfl:ic fl:ate wnh the ammal f~t, produces an acid, perhaps of the phofphoric kind, which being of a fixed nature ltes upon the bacon, giving it the yellow colour and rancid tafl:c. It is remark~ble. that the f~tpc~aerated marine acid docs not bleach li\•ing animal fubflances, at lcafl: 1t dtd not wluten.a part of my hand which I for fome minutes expofep to it. ---- NOTE XI.--STEA M-ENG IN E. ~tick moves the balanced beam, of gi"mt-birlh, lf/ields bis large limbs, and nodding jhakes tbe earth. CANTO I. 1. 261. THE expanlive force of fl:ea~ was known in fome degr~e to th~ antients, Hero. of Alexandria defcribes an application of it to produce a rotatiVe motion by the re-aCl::ton of fieam iffuiug from a fphere mounted upon an axis, through two fmall tllbes bent into tangents, and iffuing from the oppofite fides of the equ~tor.ial di~meter of the fpl:·:re, the fphere was fupplied with fieam by a pipe communtcatmg with a pan of bollmg water, and entering the fphere at one of its poles. A French writer about the year 1630 defcribes a method of railing water to the upper part of a houfe by filling a chamber with fieam, and fuffcring it to ~ondcnfc of itfel f, .but it fccms to have been mere theory, as his method was fcarcely practtctble as he dcfLnb:::s it. In 1655 the Marquis of Worcefler mentions a method of railing water by fire in Li Century of Invention s, but he feems only to have availed himfelf of the expanl!ve force and not to have known the advantages a riling from condl!nling the fl:eam by an inj eCt.:o11 of cold water. This latter and mofl important improvement feems to have been m:t lc by Capt. S::wery fomc time prior to 1698, for in that year his patent for the ufe of th:lt invention w:~s confirmed by act of parliament. This gentleman appears to h :.~ve been the firfi who reduced the machine to pract:ce, and exhibited it in an ufcful furm. Tf ;-; method confi!l:ed only inc pelling the air from a veffel by fl:cam, n.nd condcnfirg the Hearn by an injeCl::ion of cold water, which making a v:~cuurn, the prclfure of the atmofp here forced the w:;ter to afcend into the fl:eam-velfel through a pipe of 2.~ to 26 1-._-;:t Non XI. STEAM-ENGINE. high, and by the admiilion of denfe fl:cam from the boiler, forcing the water in the llcamveffcl to afcend to the height dcfired. This conl1ruCl::ion was defective becaufe it required very fl:rong veffels to refifl: th: fo:ce of the fl:eam, and becaufe an enormous quantity of fieam was condenfed by commg ll1 contaB: with the cold water in the fieam-vefTt l. . About, or foon after that time, M. Papin attempted a fl:eam-engine on fimilar princtples, but rather more Jefcctive in its confhuction. The next improvement was made very foon afterwards by Meffrs. Newcomen and Cawley of D:utmouth, it confiflcd in employing for the fieam-veffcl a hollow <;:ylinder fhut at bot~Otn and open at top, furni01ed with a pil1on Oiding ealily up and down in it, and m~de ttght by oakum or hemp, and covered with water·. This pill:on is fufpended by cha ins from one e~d of a beam, moveable upon an axis in the middle of its length, to the other end of th1s beam are fufpcrided the pump-rods. Tlte danger of burll:ing the veffcls \Vas avoided in this machine, as however high the water was to be. railed it was not neceffary to incrcafe the denfity of the fieam, but only to enbrge the diameter of the cylinder. Another advantage was, that the cylinder not being made fo cold a~ in S:~vary's . method, much lefs fl:eam was loll: in filling it after each condenfation. The machine however ll:ill remained imperfect, for the cold· water thrown into the cylinder acquired heat from the l1c:.~ m it condcnft:d, and being in a veffel exh:~nfl:ed of air it produced fleam itfelf, which in part refilled the oCl::ion of the atmofpherc on tHe pifl:on; were this remedied by throwing in more cold water, the defl:ruEl:ion 0f 11c:~m in the next filling of the cylinder woitld be proportion:~lly increafed. It has there fore in praCtice been found advifea ble not to lo:.~d thefe engines with columns of w3 ter weighing more than fcvcn pounds for each fqtt:Jre inch of the area of the piflon. The b11 lk of water, when converted into flcam, remained unknown until Mr. J. Watt, then of Glafgow, in 1764, determined it to be about 18oo times more r:~re than water. It foon occurred to Mr. Watt that a perfeCl: engine wonld be that in which no fteam fhould be conrienfcd in filling the cylinc!Lr, :tnd in which the fl:e:!m fhould be fo perfeclly cooled as to produce nearly a perfcCl:: vacuum. Mr. Watt having afcert:~inccl the degree of heat in which w:Her boi led in v:~cuo, and nnder progreilive degrees of pre 'fure, and inl1ruCl::ed by Dr. f3la k's difcovcry of latent ~l!~t, having c<1lculated the qu;wtity of cold water neceff:~ry to condenfe cert:~in quantities of fleam fo fa r as to produce the exh:wflion requireJ, he rn:1dc a communication from the cylinder to a cold vclftl previoufly exhauf!-ed of air :~nd water, into which the flc:1m wfhed by its elaflicity, :1nd became immedi:.~tely condenf..:d. He then atbptcd a cover to the cylinder, and admitted !learn above the pilton to prcfti it down inl1ead of air, :llld infle::td of applying water he ufcd oil or grcaft to fill the pores of the oakum, and to lubricate the cylinJ:::r. He next applied a pump to extract the injcCl::iot w:~ter, the ondenfcd flcam, and the :;~ir, from the condcnfing veffel, every fL·ol~e of the engine, |